This invention relates to a liquid crystal display (LCD) with a wide viewing angle, and more particularly to a LCD being capable of obtaining a wide viewing angle by simultaneously generating electric fields parallel and perpendicular to a surface of a substrate within an unit pixel area.
An in plane switching (IPS) mode LCD is developed by Hitachi, Ltd., in Japan so as to compensate the viewing angle of a TN mode LCD, which is disclosed in Asia display '95, p 577-850, "Principle and characteristic of electro-optical behaviour with in-plane switching mode". In the IPS mode LCD, as shown in FIG. 1, electrodes 2a and 2b being spaced with each other are arranged on the same front surface of the substrate 1. An homogeneous alignment layer (not shown) is formed over the front surface of the substrate where the electrodes 2a and 2b are arranged. The homogeneous alignment layer is rubbed to make a predetermined angle, for example an angle of 45 degrees with the electrons 2a and 2b. Although not shown in FIG. 1, a first polarizer which has the same polarization axis as a rubbing direction of the homogeneous alignment layer, is disposed over a rear surface of the substrate and a second polarizer which has a polarization axis parallel to the polarization axis of the first polarizer, is disposed over a rear surface of an opposite substrate.
The operation of the IPS mode LCD will be described as follows. First, if a voltage is not applied to the electrodes 2a and 2b, liquid crystal (LC) molecules 3 are arranged to make the longitudinal axes of LC molecules 3 to be in parallel to the rubbing direction of the homogeneous alignment layer. Accordingly, the picture of the LCD becomes dark state.
On the other hand, if a voltage is applied to the electrodes 2a and 2b, an electric field is generated between the electrodes 2a and 2b. Because the electrodes 2a and 2b are disposed over the same substrate, the direction of the electric field is in parallel to the surface of the substrate. According to this, LC molecules which are arranged in the rubbing direction of the homogeneous alignment layer, are twisted in the clockwise direction to make the longitudinal axes of the LC molecules to be in parallel to the direction of the electric field, if LC molecules are positive dielectric anisotropy. Therefore, the picture of the LCD becomes white state.
However, when an electric field is generated, that is when it is a white state, color of the picture in the prior IPS mode LCD becomes different according to the viewing angle due to the anisotropy of reflection index of the LC molecules. More detailedly speaking, when one views the picture of the IPS mode LCD in the X direction of FIG. 1, the one views the short axes of the LC molecules so that the picture of the LCD brings out blue color having a short wavelength rather than white color.
On the other hand, when one views the picture of the IPS mode LCD in the Y direction, the one views the longitudinal axes of the LC molecules 3b so that the picture of the LCD brings out yellow color having a long wavelength rather than white color. Therefore, the picture quality of the IPS mode LCD becomes degraded due to the color shift phenomenon. The above color shift phenomenon is detailedly disclosed in SID '97, p 929-932.